Three ‘green pea’ galaxies might have helped to end the Universe’s dark age

Astronomers using the James Webb Space Telescope (JWST) have found three tiny galaxies that could explain a watershed epoch in the history of the Universe. Reionisation was a period just 700 million years after the Big Bang when harsh radiation tore apart a ‘fog’ of hydrogen atoms hanging over the Universe, rendering stars and galaxies visible for the first time. JWST was able to observe with unprecedented clarity tiny galaxies that are so far away (and thus so old) that they were active at the time of reionisation. Three of these ancient galaxies look similar to closer ones that astronomers know well — called ‘green pea’ galaxies because of their green glow. They are prolific stellar nurseries, and emit enough energy that they might have been responsible for freeing the cosmos from its dark age.